1. Field of the Invention
The present invention relates to a non-contact torque sensor for detecting the torque transmitted to a rotating shaft.
2. Description of the Related Art
There has been known in the art a torque sensor which is constructed as shown in FIG. 6. In FIG. 6, numeral 1 designates a rotating shaft, and 3 designates a pair of amorphous magnetic alloy pieces, each formed into an elongated shape and each having magnetostrictive properties. The amorphous magnetic alloy pieces 3 are helically fastened on the rotating shaft 1 to respectively form angles of +45.degree. and -45.degree. with respect to the thrust direction thereof. Coils 4a and 4b are respectively wound concentrically in the outer sides corresponding to, and apart by a given distance from, the portions on which the amorphous magnetic alloy pieces 3 are wound and the coils 4a and 4b are connected to a differential detecting circuit 5. When a torque is transmitted to the rotating shaft 1, a strain is produced in each of the amorphous magnetic alloy pieces 3. This strain alters the permeabilities of the alloy thus changing the inductance values of coils 4a and 4b. At this time, the inductance change for the torque differs between the amorphous magnetic alloy piece 3 wound at the angle of +45.degree. with the thrust direction and the amorphous magnetic alloy piece 3 wound at -45.degree.. As a result, the magnitude and direction of the torque can be detected from the resulting differential output in the differential detecting circuit 5.
With the torque sensor constructed as described above, its sensitivity is best when only the helical amorphous magnetic alloy piece 3 of +45.degree. has a sensitivity to a right-hand torque and when only the helical amorphous magnetic alloy piece 3 of -45.degree. has a sensitivity to a left-hand torque, respectively. However, due to the nonuniform stress, etc. caused during the adhesion, the respective alloy pieces 3 are strained by either positive or negative torques, thus deteriorating the sensitivity of the torque sensor. There is another disadvantage in that the amorphous magnetic alloy pieces 3 are fastened on the surface of the rotating shaft 1 with an adhesive, thus failing to ensure a sufficient adhesion strength.